It's not that Carly would rather have the attention,t's just that she'd rather the guys like Anna because how she is... not for her outer appearance. Carly's the older sister who no one would want to be near, because she wants to be the kind of person who people notice...Visually, and in her case, neon baggy shirts and a broom skirt--- not very attractive. What Carly doesn't realize about Anna, is that she looks up to her, wishes that she was as skinny as her, as smart as her, as beautiful as her, and lastly, her friends, I know pathetic, but she doesn't have any real friends... just her wannabes.
Anna could easily form a clique with the girls who trail around her, but that wouldn't be the same as Carly's LOL best friends, and so whenever she tries to hang out with them, Carly starts getting defensive and nothing works out the way she expected. Anna wants to be like Carly, but not even as youremybestfriend but as an exact clone of her, which Carly does not understand, knowing about all the fame she gets at school.
At the end Anna does something so bad that Carly finally gets how Anna feels and they become the bffs forever.